Method of preparing fine hydrosulfite



United States Patent 3 205 038 METHOD OF PREPAiiIN FINE HYDROSULFITE Virgil L. Hansley, Cincinnati, Louis F. Moormeier, White Oak, and Stuart Schott, Cincinnati, Ohio, asslgnors to National Distillers and Chemical Corporation, New York, N .Y., a corporation of Virginia No Drawing. Filed Aug. 23, 1961, Ser. No. 133,323 3 Claims. (Cl. 23116) This invention relates broadly to an alloy composition, its uses, and its preparation. More particularly, it relates to a sodium-zinc composition, its uses, and its preparation.

At the present time zinc dust, having a particle size of about 200 to 325 mesh, is used commercially when the reaction calls for the use of zinc in reactive form. The use of zinc dust, however, has several disadvantages. In the first place, zinc dust, obtained commercially by distilling virgin or by products .zinc, is relatively expensive. In addition, fire and explosion hazards are involved in the handling and reaction of zinc dusts. Furthermore, the use of zinc dust requires a special reaction zone that can handle finely-divided material.

It is an object of this invention to provide an improved form of reactive or chemically active zinc.

Another object of this invention is to provide a reactive form of zinc which eliminates the hazards involved in employing zinc dust as a reactant.

A further object of this invention is .to provide a method for producing zinc hydrosulfite by reacting sulfur dioxide under conventional operating conditions with a sodiumzinc alloy composition, the activated zinc composition of this invention, prepared by fusing sodium with virgin or by-produet zinc.

Other objects will become apparent from the ensuing detailed description of the invention.

It has now been found that the disadvantages involved in the use of zinc dust can be overcome by the use of a solid sodium-zinc alloy composition. The use of such an alloy composition, for example, in the reaction with S0 to yield ZnS O while resulting in products which are comparable to current commercial products in both quality and quantity has a number of important advantages over the use of conventional zinc dust.

One advantage is economics: the cost of zinc dust, prepared by distilling by-product zinc, is considerably more than the cost of a sodium-zinc alloy composition, prepared for example by melting together fresh or by-product zinc and sodium.

In addition, because of the sodium content of the sodium-zinc alloy composition, it has been found that the alloy composition is more reactive than conventional zinc dust toward materials like sulfur dioxide. Due to this increased activity, the rates of reaction to give, for example, zinc hydrosulfite of a sodium-zinc alloy composition having a mesh size of about 60 to 325 are substantially equivalent to those of finer mesh-size zinc dust. In many commercial applications it is also possible to use relatively large pieces, for example, up to about 2 inches in diameter, of sodium-zinc alloy composition, thus eliminating the necessity for an elaborate grinding procedure. If, however, a more finely-divided material is desired, the alloy composition can be comminuted to dust by any simple technique, such as by mortar and pestle or by a hammer mill operation.

Another important advantage which the use of a sodium-zinc alloy composition has over zinc dust is the fact that by using the alloy composition the fire and explosion hazards which are involved in the handling of such metal dusts are largely avoided. 1

The sodium-zinc alloy composition can be made by any ice convenient method. Most commonly it is prepared by melting together sodium and zinc metal, for example, ingot zinc, galvanizers zinc dross, die-casters zinc Waste. The resulting sodium-zinc alloy composition is usually cast into an ingot which is then cooled. The resulting casting can then be comminuted into pieces having a particle size up to about 2 inches in diameter, and preferably having a particle size between about 200 mesh and 1 inch. It is also possible to obtain pieces of the desired size by agitating the crystallizing alloy through its solidification temperature.

The amount of sodium in the sodium-zinc alloy composition may vary widely, but in general a sodium content of about 0.5 to about 4.0 weight percent is satisfactory and a sodium content of about 1 to 3.5 percent is preferred. An alloy composition containing up to about 4 percent of sodium is sufiiciently brittle to permit easy grinding, which is another advantage of the sodium-Zinc alloy of this invention. It will be understood, however, that an ingot formed from the sodium-zinc alloy may be sold as such and that the alloy may be comminuted later at the point of use. A sodium content higher than about 40% results in a product which contains a malleable free sodium phase, and because of this can be ground only with difficulty. Also, an alloy composition having a sodium content higher than about 4 percent tends to react with oxygen and moisture in the air, resulting in an alkaline and moist material when in contact with moist air.

The chemically-active zinc of this invention, that is, zinc in the form of a sodium-zinc alloy composition, is advantageously used in many applications. For example, to obtain zinc hydrosulfite, the sodium-zinc alloy composition can be reacted with sulfur dioxide in aqueous solution at a temperature between about 0 and 50 C., and preferably between about 30 and 35 C. The pH is usually maintained between about 3.5 and 5.5. The zinc hydrosulfite is continually withdrawn from the system.

The preparation of zinc hydrosulfite may be effected in any suitable conventional reaction vessel adapted for carrying out such a reaction, such as static beds or slowly agitated beds, for example, a rotating drum reactor, and with conventional operating conditions, except that a so- ,dium-zinc alloy composition as embodied herein is used instead of the zinc dust of commerce.

Zinc hydrosulfite so produced can be converted into sodium hydrosulfite by any convenient procedure. Most commonly it is reacted with sodium hydroxide or sodium carbonate at about 0 to about 65 C.

Zinc hydrosulfite is also important industrially as a bleaching agent for groundwood, paper and pulp, and other cellulosic materials.

Reactive or chemically active zinc in the form of the sodium-zinc alloy composition of this invention may also be used to replace zinc dust in the following additional reduction applications:

(1) Reduction of benzophenone'to produce benzhydrol.

(2) Reduction of nitrobenzene to produce azobenzene.

(3) Reduction of para-toluene sulfonyl chloride to pro.- duce the sodium salt of para-toluene sulfinic acid.

(4) Reduction of benzoin to produce trans-stilbene. It will also be understood that the sodium-zinc a-l-loy may be used in place of zinc dust in many other chemical reactions, which ordinarily employ the latter material, to attain equivalent or better results.

The following examples are presented only to illustrate this invention and are not intended to limit it. Obvious modification will occur to persons skilled in the art. All parts are given by weight unless otherwise specified.

EXAMPLE I A charge of 364 parts of by-product zinc from diecasting operations was heated with 14.6 parts (4 percent) 3 of sodium under 100 parts each of NaCl and CaCl for one hour, the temperature reaching 800 C. at the end of that time. Intermittent agitation was employed during the heating. Flame photometry showed that the resulting alloy composition obtained 2.46 to 2.97 percent of sodium.

EXAMPLE II A sodium-zinc alloy composition, prepared as in Example I, was grouped to a particle size about 200 mesh, and 4.0 gram atoms of the ground alloy composition was reacted With 4.11 moles of sulfur dioxide in 1,200 parts of air-free water at 45-50 C. for 54 minutes at a pH of 4.7-5.3. Titration of the resulting filtered zinc hydrosulfite solution showed 334 parts of zinc hydrosulfite, corresponding to a yield of 96.5 percent, based on the zinc, or 86.9 percent, based on the sulfur dioxide.

EXAMPLE III A sodium-zinc alloy composition (4.642 parts of /2 to l" lumps), containing 1.6 percent of sodium and made from galvanizers zinc dross, was reacted in 1,600 parts of air-free water with sulfur dioxide, fed to the system in 100-gram increments. The pH of the system was maintained at 3.0-3.8; the temperature was held at 29-32 C. After each 100-gram addition of the sulfur dioxide, a sample of product was removed and analyzed for ZnS O The following table shows the yields for each 100-gram addition of sulfur dioxide and the over-all yield to that point.

To demonstrate that the use of sodium-zinc alloy compositions as a replacement for zinc dust in producing zinc hydrosulfite does not achieve the advantages of economy and safety at the expense of quantity of product, Exam-' ple IV was run with zinc dust.

EXAMPLE IV Zinc dust (4.04 gram atoms) having a particle size of about 375 mesh was reacted with 4.12 moles of liquid sulfur dioxide in air-free water at 4350 C. for 66 minutes at a pH of 4.5-5.1 in a recirculation system blanketed with nitrogen. After filtration to recover unreacted zinc, titration of the resulting zinc hydrosulfite solution showed 364 parts of ZnS O corresponding to a yield of 93.6 percent, based on the zinc, or 91.5 percent, based on the sulfur dioxide.

A comparison of the results of Example H, using a sodium-zinc alloy composition, with those of this exam ple using zinc dust, is tabulated below:

In the following examples the sodium-zinc alloy of this invention having a particle size of about 200 mesh was compared, other than in Example VII, to commercial zinc dust having a particle size of about 325 mesh.

EXAMPLE V A charge of 100 g. of benzophenone, 100 g. of powdered caustic soda, 1000 ml. of 95% ethanol and 101.6 g. of zinc-sodium alloy (2% Na) were charged into a stirred two-liter pyrex reaction vessel. A reflux condenser was provided and, during the course of the reaction, the temperature increased from ambient temperature of 26 C. to 72 C. in 15 minutes and fell off slowly thereafter a 3-hour reaction period. When cool, zinc residues were removed by filtration and the filtrate stirred into 5 liters of ice water containing 213 ml. of hydrochloric acid. Separated product was 93 g., representing a 92.4% yield of benzhydrol M.P. 65 C.

EXAMPLE VI Into a 3-neck, 3-liter flask, equipped with a stirrer and reflux condenser, were charged 1125 ml. of methanol, 125 g. of nitrobenzene, 162.5 g. of NaOH in 325 ml. of water, and 132.5 g. of commercial zinc dust. Heat was applied, and the mixture refluxed for 12 hours. The reaction mixture was filtered hot from zinc residues and the filtrate concentrated by evaporating off most of the methanol. Upon cooling, orange-red crystals of azobenzene separated out. The dried crystallized product amounted to 66.7 g. (M.P. 66-68 C.), a yield of 72.2%.

In a parallel experiment, 125 g. of nitrobenzene, 162.5 g. of caustic soda in 375 ml. of water, 1125 m1. of methanol, and 135.4 g. of zinc-sodium alloy (2.2% Na) were reacted in an analogous manner. After working up the reaction mixture, 57.9 g. of recrystallized azobenzene, M.P. 66-68 C., was recovered.

EXAMPLE VII Para-toluene sulfonyl chloride was reduced with zincsodium alloy (2.2% Na) by adding the dry sulfonyl chloride slowly to the alloy powder suspended in distilled Water at C. With temperature controlled at 80 C., the whole charge of chloride (215 g.) was reacted with the alloy in about 13 minutes. After ten minutes additional heating to C., 62.5 ml. of 12N NaOH solution was added followed by dry sodium carbonate until the reaction was alkaline. The filtrate was then allowed to evaporate to 250 cc. Upon chilling, 31.5 g. (dry Wt.) of p-toluene sulfinic acid sodium salt separated out.

EXAMPLE VIII Into a 4-liter pyrex beaker equipped with a stirrer was placed 500 ml. of water and 50 g. of mercuric chloride. The charge of zinc dust was added slowly to this mixture to effect amalgamation of the zinc. After 30 minutes the zinc amalgam was filtered off and washed with water. The amalgam was then added to cold methanol in which was dissolved g. (0.48 mol.) of benzoin. Then 500 cc. of concentrated hydrochloric acid was added with continued cooling by an ice-water bath. This part of the procedure required 3.5 hours. Two liters of water were added to precipitate the product together with the zinc sludge. Transstilbene was extracted from the sludge on the filter using hot ethanol. Upon cooling, 16.9 g. of trans-stilbene, M.P. 116121 C., crystallized out. This was a recovered yield of 19.9%. The above procedure was repeated, except that ground zinc-sodium alloy (2.2% Na) was used instead of zinc dust. The same yield of 16.9 of trans-stilbene (M.P. 11612l C.) was isolated.

The above data show that the sodium-zinc alloys of this invention have many uses and may, in numerous instances, be employed in place of zinc dust to attain analogous results while avoiding the numerous difliculties encountered when using the conventional zinc dust.

While particular embodiments of this invention are shown above, it will be understood that the invention is,

obviously subject to variations and modifications without departing from its broader aspects.

What is claimed is:

1. In a method for the preparation of zinc hydrosulfite by reacting reactive zinc with sulfur dioxide in aqueous solution at a temperature between about 0 and 50 C., the improvement which comprises using reactive zinc in the form of a sodium-zinc alloy composition having a particle size from about /2 inch up to about 2 inches and a sodium content of about 0.5 to 4.0 weight percent.

2. The improvement of claim 1 wherein the particle size of the alloy composition is between about /2 and 1 inch.

3. The improvement of claim 1 wherein the sodium References Cited by the Examiner UNITED STATES PATENTS West 23-129 Lance 23-l29 Wemple et al 75-l78 Anstey et al. 75178 Luehdemann 23-116 Schechter 7586 Wyatt 7586 FOREIGN PATENTS content of the alloy composition is between about 1 and 15 MAURICE BRANDISI Primary Examiner- RAY K. WINDHAM, Examiner.

3.5 weight percent. 

1. IN A METHOD FOR THE PREPARATION OF ZINC HYDROSULFITE BY REACTING REACTIVE ZINC WITH SULFUR DIOXIDE IN AQUEOUS SOLUTION AT A TEMPERATURE BETWEEN ABOUT 0* AND 50*C., THE IMPROVEMENT WHICH COMPRISES USING REACTIVE ZINC IN THE FORM OF A SODIUM-ZINC ALLOY COMPOSITION HAVING A PARTICLE SIZE FROM ABOUT 1/2 INCH UP TO ABOUT 2 INCHES AND A SODIUM CONTENT OF ABOUT 0.5 TO 4.0 PERCENT. 